We'll turn now to the latest on the high-profile trial of zimmerman skim acgeorge zimmerman, week two beginning with the star witness, the lead investigator in the case expected to take the stand for the prosecution and abc's matt gutman once again in sanford, florida, with the latest. Good morning to you, matt. Reporter: Good morning, josh. In just a couple of hours, jurors are expected to hear from that lead investigator, chris serino. He was suspicious of the claim he acted in self-defense. That's why he recommended manslaughter charges against zimmerman. His testimony could be the best last chance for the prosecution here. This morning jurors are expected to hear from the man in the time, the cop, chris serino who wanted manslaughter charges against him. The lead homicide detective is walking zimmerman through his reenactment. Zimmerman telling him he shot martin in self-defense. My foot was on the cement and he just kept -- Reporter: Two days later. This questioning -- you know the name of the person that died? Tavon. Trayvon. Trayvon martin. Trayvon benjamin martin. He was born in 1975. A kid with a future. A kid with folks that care. Reporter: At the time serino knew the case better than anyone else and three weeks after the shooting as protests rocked sanford, he recommended manslaughter charges for zimmerman, including the encounter was ultimately avoidable by zimmerman if zimmerman had remained in his vehicle. But the state attorney then felt there wasn't enough evidence to convict, weeks of protests and high school walkouts followed, and zimmerman was eventually arrested. Now, there was some fallout at the sanford police department. The police chief was fired. Chris serino was moved to the nighttime patrol and afterwards he told the fbi he felt pressured by his colleagues to come up with that manslaughter charge, so a witness who comes up for the prosecution may well end up benefiting the defense when all is said and done, josh.

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